Solid-state imaging device, method of fabricating solid-state imaging device, and camera

ABSTRACT

A solid-state imaging device receiving incident light from a backside thereof. The imaging device includes a semiconductor layer on which a plurality of pixels including photoelectric converters and pixel transistors are formed, a wiring layer formed on a first surface of the semiconductor layer, a pad portion formed on a second surface of the semiconductor layer, an opening formed to reach a conductive layer of the wiring layer, and an insulating film extendedly coated from the second surface to an internal side-wall of the opening so as to insulate the semiconductor layer.

RELATED APPLICATION DATA

This application is a continuation of U.S. patent application Ser. No.12/354,457, filed Jan. 15, 2009, the entirety of which is incorporatedherein by reference to the extent permitted by law. The presentapplication claims priority to Japanese Patent Application No. JP2008-010904 filed in the Japanese Patent Office on Jan. 21, 2008, theentirety of which also is incorporated by reference herein to the extentpermitted by law.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a backside-illuminated solid-state imagingdevice, a method of fabricating the backside-illuminated solid-stateimaging device, and a camera.

2. Description of the Related Art

In a CMOS type solid-state imaging device, there has been disclosed abackside-illuminated solid-state imaging device for improvingphotoelectric conversion efficiency and sensitivity to incident light.In the backside-illuminated solid-state imaging device, light isilluminated from backside of the solid-state imaging device. Thebackside-illuminated solid-state imaging device is configured to includea semiconductor substrate on which photodiodes as photoelectricconverters, pixel transistors, a plurality of wiring layers forming asignal circuitry, and the like are formed (see Japanese UnexaminedPatent Application Publication No. 2005-347707, and Japanese UnexaminedPatent Application Publication No. 2005-353631).

The backside-illuminated solid-state imaging device includes a padportion formed on a rear side of the semiconductor substrate that cansupply predetermined electrical potential to a multilayer interconnectformed on a front-surface side of the semiconductor substrate.

FIG. 1 is a schematic cross-sectional configuration diagram illustratinga backside-illuminated solid-state imaging device according to therelated art. The cross-sectional configuration diagram in FIG. 1specifically illustrates a region that includes a pad portion 60 formedin a peripheral region of a rear side of the backside-illuminatedsolid-state imaging device.

The backside-illuminated solid-state imaging device 70 includes animaging region in which photodiodes 54 each used as a photoelectricconverter and a plurality of pixels including pixel transistors (MOStransistors), a peripheral circuitry are formed on a semiconductor Silayer 53, and a pad portion 60 formed in a peripheral region of a rearside thereof. Although not shown in the figure, the pixel transistorseach forming a pixel are formed on a front-surface side of the Si layer53. Further, multi-layer interconnects 52 (e.g., Cu interconnects) and aplurality of wiring layers 51 including a wire-bonding AL interconnect52 a are formed on a surface of the Si layer 53 via an interlayerdielectric 61. A supporting substrate 50 formed of a silicon substrateis formed on a front-surface side of the plurality of wiring layers 51.

In contrast, an insulating film 55 used as an antireflective film, ashield film 56, and a passivation film 57 are multiply layered in thisorder on a rear side of the Si layer 53. Further, on-chip color filtersare formed on the passivation film 57 corresponding to the imagingregion, and on-chip microlenses 53 are formed on the passivation film57. The imaging region includes an optical black region formed outsideof an effective pixel region for specifying black levels of images.Pixels and color filters similar to the pixels in the effective pixelregion are formed in the optical black region. The shield film 56 isformed over an entire surface including other pixel transistors andperipheral circuitries except for light-receiving portions in theeffective pixel region, namely, the photodiodes 54 and pad portions 60.

The pad portion 60 includes an opening 62 to expose the AL interconnect52 a connected to predetermined interconnects 52 of the plurality ofwiring layers 51. Specifically, after the on-microchiplenses have beenformed, an opening 62 is formed such that desired Al interconnects 52 aare exposed from a rear surface of the backside-illuminated solid-stateimaging device 70 towards a front-surface thereof on which themultilayer interconnection layer 51 is formed, thereby forming the padportion 60 for taking out an electrode. In this process, the pad portion60 is formed by etching the Si layer 53 including photodiodes 54 formedthereon, an insulating film 55 formed on an incident light surface ofthe Si layer 53, an interlayer dielectric 61 of the plurality of wiringlayers 51, and the like. In the pad portion 60 formed in this manner,for example, Au fine wires (so called bonding wires) 63 are connected toAl interconnects 52 a (wire-bonding) that are exposed from the opening62.

However, in the related art backside-illuminated solid-state imagingdevices, since the Si layer 53 is exposed from an internal sidewall ofthe pad portion 60, the Si layer 53 and the Au fine wires 63 are broughtinto contact when the Au fine wires 63 are wire-bonded to the Alinterconnects 52 a in the pad portion 60. Therefore, current is likelyto flow between a well region (e.g., p-type well region) for the Au finewires 63 having ground potential and a region having differentpotential. That is, leak current flows from the Au fine wires 63 to theSi layer 53.

The interlayer dielectric 61 of the plurality of wiring layers 51 isexposed from the internal sidewall of the opening 62 forming the padportion 60. The interlayer dielectric 61 includes metal used as theinterconnects 52 forming a signal circuitry. Thus, only providing theinterlayer dielectric 61 that is exposed from the opening 62 may not besufficient to prevent the interconnects 52 from absorbing moisture. Thatis, the interconnects 52 may deteriorate under a high-humidityenvironment. In the cutting-edge CMOS process, an insulating film with asmall dielectric constant (a Low-κ dielectric) is used as the interlayerdielectric 61 of the plurality of wiring layers 51; however, a filmproperty of the Low-κ dielectric may also deteriorate under suchhigh-humidity environment, thereby exhibiting no moisture resistance inthe interlayer dielectric 61.

Japanese Unexamined Patent Application Publication No. 2005-347707discloses a pad portion configuration including an insulating filmformed on the sidewall thereof. However, in this configuration, sincethe insulating film is only formed for the pad portion, the number ofsteps for fabricating backside-illuminated solid-state imaging devicesmay increase. Moreover, the pad portion may be coated with an organicfilm, however, the organic film may not be able to cover the pad portionsufficiently (not enough coverage), thereby exhibiting not enoughreliability.

Further, since the related art shield film used in thebackside-illuminated solid-state imaging device is electricallyfloating, electrical potential is not stabilized. As a result, theelectrical potential of the shield film may cause an adverse effect onpixels of the solid-state imaging device.

SUMMARY OF THE INVENTION

Embodiments of the invention intend to provide a solid-state imagingdevice that exhibits excellent reliability, a method of fabricating thesolid-state imaging device, and a camera.

An embodiment of the invention intends to provide a solid-state imagingdevice receiving incident light from a backside thereof. The imagingdevice includes a semiconductor layer on which a plurality of pixelsincluding photoelectric converters and pixel transistors are formed, aplurality of wiring layers formed on a first surface of thesemiconductor layer, a pad portion formed on a second surface of thesemiconductor layer, an opening formed to reach a conductive layer ofthe plurality of wiring layers, and an insulating film extendedly coatedfrom the second surface to an internal side-wall of the opening so as toinsulate the semiconductor layer.

An embodiment of the invention also provides a method of fabricating asolid-state imaging device. The method includes forming a plurality ofwiring layers on a first surface of a semiconductor layer on which aplurality of pixels including photoelectric converters and pixeltransistors, forming an opening corresponding to a pad portion of asecond surface of the semiconductor layer to reach a conductive layer ofthe plurality of wiring layers, and forming an insulating filmextendedly coated from the second surface to an internal side-wall ofthe opening so as to insulate the semiconductor layer.

An embodiment of the invention further provides a camera including asolid-state imaging device, an optical lens, and a signal processor. Inthe camera, the solid-state imaging device includes a semiconductorlayer on which a plurality of pixels including photoelectric convertersand pixel transistors are formed, a plurality of wiring layers formed ona first surface of the semiconductor layer, a pad portion formed on asecond surface of the semiconductor layer, an opening formed to reach aconductive layer of the plurality of wiring layers, and an insulatingfilm extendedly formed from the second surface to an internal side-wallof the opening so as to coat the semiconductor layer.

In an embodiment of the invention, the insulating film is extendedlyformed from the surface of the semiconductor layer to the internalside-wall of the opening of the pad portion formed on the solid stateimaging device to insulate the semiconductor layer, advert effect on thesemiconductor layer and the plurality of wiring layers may be prevented.

According to an embodiment of the invention, since the insulating filmis extendedly coated from the surface of the semiconductor layer to theinternal side-wall of the opening of the pad portion, the advert effecton the semiconductor layer and the plurality of wiring layers may beprevented, thereby improving product reliability of the solid-stateimaging device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-section configuration diagram illustrating asolid-state imaging device according to the related art.

FIG. 2 is a schematic diagram illustrating a solid-state imaging deviceaccording to a first embodiment of the invention.

FIG. 3 is a schematic cross-sectional configuration diagram illustratingmain parts of the solid-state imaging device according to the embodimentof the invention.

FIG. 4 is a schematic cross-section configuration diagram illustrating apad portion used in the solid-state imaging device according to theembodiment of the invention.

FIG. 5 is a schematic cross-sectional configuration diagram illustratinga ground connection pad portion used in the solid-state imaging deviceaccording to the embodiment of the invention.

FIGS. 6A, 6B are respectively a cross-section configuration diagramalong the line A-A, and a cross-sectional configuration diagram alongthe line B-B (part one) of the solid-state imaging device according tothe embodiment of the invention.

FIGS. 7A, 7B are respectively a cross-section configuration diagramalong the line A-A, and a cross-sectional configuration diagram alongthe line B-B (part two) of the solid-state imaging device according tothe embodiment of the invention.

FIGS. 8A, 8B are respectively a cross-section configuration diagramalong the line A-A, and a cross-sectional configuration diagram alongthe line B-B (part three) of the solid-state imaging device according tothe embodiment of the invention.

FIGS. 9A, 9B are respectively a cross-section configuration diagramalong the line A-A, and a cross-sectional configuration diagram alongthe line B-B (part four) of the solid-state imaging device according tothe embodiment of the invention.

FIGS. 10A, 10B are respectively a cross-section configuration diagramalong the line A-A, and a cross-sectional configuration diagram alongthe line B-B (part five) of the solid-state imaging device according tothe embodiment of the invention.

FIGS. 11A, 11B are respectively a cross-section configuration diagramalong the line A-A, and a cross-sectional configuration diagram alongthe line B-B (part six) of the solid-state imaging device according tothe embodiment of the invention.

FIGS. 12A, 12B are respectively a cross-section configuration diagramalong the line A-A, and a cross-sectional configuration diagram alongthe line B-B (part seven) of the solid-state imaging device according tothe embodiment of the invention.

FIGS. 13A, 13B are respectively a cross-section configuration diagramalong the line A-A, and a cross-sectional configuration diagram alongthe line B-B (part eight) of the solid-state imaging device according tothe embodiment of the invention.

FIGS. 14A, 14B are respectively a cross-section configuration diagramalong the line A-A, and a cross-sectional configuration diagram alongthe line B-B (part nine) of the solid-state imaging device according tothe embodiment of the invention.

FIGS. 15A, 15B are respectively a cross-section configuration diagramalong the line A-A, and a cross-sectional configuration diagram alongthe line B-B (part 10) of the solid-state imaging device according tothe embodiment of the invention.

FIGS. 16A, 16B are respectively a cross-section configuration diagramalong the line A-A, and a cross-sectional configuration diagram alongthe line B-B (part 11) of the solid-state imaging device according tothe embodiment of the invention.

FIGS. 17A, 17B are respectively a cross-section configuration diagramalong the line A-A, and a cross-sectional configuration diagram alongthe line B-B of a solid-state imaging device according to a secondembodiment of the invention.

FIG. 18 is a schematic diagram illustrating a camera according to anembodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the invention will be described below with reference toaccompanying drawings.

FIG. 2 is a schematic diagram illustrating a solid-state imaging deviceaccording to a first embodiment of the invention. A solid-state imagingdevice according to embodiments of the invention is abackside-illuminated CMOS solid-state imaging device.

A solid-state imaging device according to an embodiment of the inventionis configured to include imaging region 3, peripheral circuitries 6, 7,pad portions 5.

The imaging region 3 includes a matrix of numerous unit pixels, andaddress lines arranged in rows, and signal lines arranged in columns.The imaging region 3 includes an effective pixel region 3 a and anoptical black region 3 b that determines a black level of each pixel.

The optical black region 3 b also includes similar pixels as thoseincluded in the effective pixel region 3 a. The pixels in the opticalblack region 3 b are arranged outside of the effective pixel region 3 a.An entire region of the solid-state imaging device, excluding thephotoelectric converters (light-receiving portion) of the effectivepixel region 3 a and the pad portions 5, is covered with the shieldfilm.

Each pixel in the imaging region 3 includes the photoelectric convertersuch as a photodiode and a plurality of pixel transistors (MOStransistors). Each of the pixel transistors may include fourtransistors, examples of which include a transferring transistor, aresetting transistor, an amplifying transistor, and a selectingtransistor. Alternatively, each pixel transistor may simply includethree transistors, examples of which include the transferringtransistor, the resetting transistor, and the amplifying transistor. Or,each pixel transistor may include other transistors.

FIG. 3 shows an example of a cross sectional structure of the unitpixel. In this example, a unit pixel 31 a is formed by forming a secondconductive p-type pixel separating region 32, a photodiode (PD) 11 as aphotoelectric converter and a plurality of pixel transistors Tr1, Tr2 ona first conductive n-type silicon semiconductor layer 10. The photodiode11 includes an n-type semiconductor layer 10 surrounded by a p-typepixel separating region 32 and a relatively deeply formed p-typesemiconductor well region 35 in which the pixel transistors Tr1 and Tr2are formed, and p+ accumulation layers 33, 34 for controlling darkcurrent on both front-surface and rear-surface sides of the solid-stateimaging device. The n-type semiconductor layer 10 forming the photodiode11 includes a highly concentrated n+ charge-storing region 10 a and alowly concentrated n-type region 10 b forming the n-type semiconductorlayer 10. The n-type region 10 b of the n-type semiconductor 10 isextendedly formed below the p-type semiconductor well region 35 in whichthe pixel transistors Tr1, Tr2 are formed.

The pixel transistors Tr1, Tr2, for example, each include fourtransistors as described earlier. In the figure, Tr1 indicates atransferring transistor, and Tr2 indicates other transistors such as aresetting transistor, an amplifying transistor, or a selectingtransistor. The pixel transistor Tr1 includes the n+ source-drain region37 of floating diffusion, the n+ charge-storing region 10 a of thephotodiode 11, and a gate electrode 41 formed via a gate insulatingfilm. The pixel transistor Tr2 includes a paired source drain regions38, 39 and a gate electrode 42.

A plurality of wiring layers 9 having interconnects M1 to M4 multiplylayered via an interlayer dielectric 14 is formed on a front-surface ofthe semiconductor layer 10, and a supporting substrate 8 formed such asa silicon substrate is bonded to the plurality of wiring layers 9. Theinterconnects M1 to M3 in the first to third layers forms a signalcircuitry which is formed of Cu interconnects by damascene process. Theinterconnect M4 in the fourth layer is a conductive layer including Alinterconnects that is connected with Au fine wires wire-bonding process.

An insulating film used as antireflective film 45 is provided with arear side of the semiconductor layer 10. The antireflective film 45 isformed of a film stack having a nitride film (SiN) 12 and a siliconoxide (SiO₂) film 17 stacked on the semiconductor layer 10 in thisorder. The shield film 18 is formed on the antireflective film 45excluding a light-receiving portion for a photodiode, and a passivationfilm 19 is further formed over the shield film 18. The passivation film19 may be formed of a planarized film. The shield film 18 is formed of ametal film. Further, an on-chip color filters CF for primary colors ofred (R), green (G), blue (B) are formed on the passivation film 19corresponding to the imaging region, and on-chip microlenses 25 areformed on the on-chip color filters CF.

In contrast, although not shown in the figure, peripheral circuitries 6,7 each are configured to include a vertical driving circuitry, a columnsignal processing circuitry, a horizontal driving circuitry, an outputcircuitry, a control circuitry, and the like. The control circuitrygenerates a clock signal or control signal that controls fundamentaloperation of the vertical driving circuitry, column signal processingcircuitry, and horizontal driving circuitry based on a verticalsynchronizing signal, a horizontal synchronizing signal, and a masterclock; and input the generated signals into the vertical drivingcircuitry, column signal processing circuitry, horizontal drivingcircuitry, and the like. The vertical driving circuitry may be formed ofa shift register that sequentially selects and scans pixels per columnin the imaging region 3 in a vertical direction, and then supplies tothe column signal processing circuitry signal charge generated based onan amount of light received by the photoelectric converter for eachpixel via vertical signal lines. The column signal processingcircuitries are arranged for each column of the pixels, and signalsoutput by the pixels per row is signal-processed per pixel column suchas noise cancellation or signal amplification with signals output by theblack reference pixels in the optical black region. A horizontalselecting switch is connected between horizontal signal lines in anoutput stage of the column signal processing circuitry. The horizontaldriving circuitry may be formed of a shift register that sequentiallyselects pixels per column of the column signal circuitry by sequentiallyoutputting horizontal pulses, and then causes each of the column signalprocessing circuitries to output the pixel signals to the horizontalsignal lines. The output circuitry signal processes the signalssequentially supplied from each of the column signal processingcircuitries via the horizontal signal lines, and outputs the resultingsignals.

Since the solid-state imaging device 1 of the embodiment isbackside-illuminated type, a plurality of pad portions 5 are formedaround the imaging region thereof such that interconnects formed on thefront-surface of the solid-state imaging device 1 can be taken out ofthe pad portions 5. One of the pad portions 5 is used as a groundinterconnect (hereinafter called “ground connecting pad portion”) 5 g.In the ground connecting pad portion 5 g, a ground interconnect isconnected with the shield film 18 as will be described later. The groundconnecting pad portion 5 g includes an opening formed in the same stepas the step of forming an opening in the pad portion 5.

FIG. 4 illustrates a cross sectional structure of the pad portion 5along A-A line in FIG. 2. According to the solid-state imaging device 1of the embodiment, insulation is securely formed so as to separatebonding wires, such as Au fine wires wire-bonded with the pad portions5, from the semiconductor layer 10 in the pad portion 5 as shown in FIG.4. FIG. 5 illustrates a cross sectional structure of the groundconnecting pad portion 5 g along B-B line in FIG. 2. As shown in FIG. 5,in the ground connecting pad portion 5 g, ground potential is providedwith the shield film 18, and insulation is securely formed to separatethe shield film 18 with the ground potential from the semiconductorlayer 10.

As shown in FIG. 4, adequate Cu interconnects of M1, M2, and M3 areconnected in the plurality of wiring layers 9. In this embodiment, theinterconnects M1 to M3 are connected, and interconnects M3 and M4(conductive layer) are connected. The interconnect M4 is extended to aportion corresponding to the pad portion 5. The pad portion 5 includesan opening 16 such that the Al interconnect M4 is exposed from thesurface of the on-chip microlens film 21, on which the on-chipmicrolenses 25 are formed. A silicon oxide film 17, passivation film 19,and on-chip microlens film 21 that form an antireflective film areprovided 10 as an insulating film on an internal side-wall of theopening 16 so as to cover the semiconductor layer 10. The Alinterconnect M4 is exposed from a bottom of the opening 16. The shieldfilm 18 is not formed on a region corresponding to the opening 16.

Bonding wires such as Au fine wires 24 are wire-bonded with the Alinterconnect M4 exposed from the bottom face of the pad portion 5. Inthe pad portion 5, an insulating film including the silicon oxide film17, passivation film 19, and on-chip microlens film 21 are extendedlyformed such that the semiconductor layer 10 on the internal side-wall ofthe opening 16 is insulated, thereby preventing contingent current leak.The interconnects M1 to M4 of the plurality of wiring layers 9 and theinterlayer dielectric 14 can be prevented from absorbing moisture. Thus,the reliability of the solid-state imaging device can be improved.

As shown in FIG. 5, of the interconnects M1 to M4 (not shown in thefigure) in the plurality of wiring layers 9, the ground interconnect(conductive layer) 15 connected to the predetermined interconnects towhich ground potential is supplied is extended to a positioncorresponding to a position of the ground interconnecting pad portion 5g. The ground interconnect 15 is formed of Al fine wires, and formedsimultaneously with the interconnect M4 in the same layer thereof. Theground interconnecting pad portion 5 g includes the opening 16 formedfrom the surface of the on-chip microlens film 21 to the groundinterconnect 16, the silicon oxide film 17 used as an antireflectivefilm in the imaging region on the internal side-wall of the opening 16so as to insulate the semiconductor layer 10, and an extended portion 18a of the shield film 18 formed from internal side-wall of the opening 16to the bottom thereof so that the shield film is electrically connectedto the ground interconnect 15. Further, the passivation film 19 and themicrolens film 21 are also extendedly formed on the internal side-wallof the opening 16. Although not shown in the figure, the groundinterconnect 15 is electrically connected to the pad portion 5 to whichthe ground potential is supplied. A configuration of the pad portion 5to which the ground potential is supplied is substantially the same asthat of the pad portion 5 in FIG. 4.

In the ground connecting pad portion 5 g having such a configuration,since the extended portion 18 a of the shield film 18 is electricallyconnected to the ground interconnect 15 extended to the opening 16, theshield film 18 is set to the ground potential and is electricallystabilized. Further, since the silicon oxide film 17 forming theantireflective film and extendedly formed on the internal side-wall ofthe opening provides insulation between the semiconductor layer 10 andshield film 18, the semiconductor layer 10 is securely insulated fromthe shield film 18. Since the passivation film 19 and on-chip microlensfilm 21 are extendedly formed on the internal side-wall of the opening16, absorption of moisture in the interconnects M1 to M4 in theplurality of wiring layers 9 can be prevented. Thus, the reliability ofthe solid-state imaging device can be improved.

Next, a method of fabricating the aforementioned solid-state imagingdevice 1, in particular, a method of fabricating the pad portion havinga cross sectional configuration along A-A and B-B in FIG. 2 is describedwith reference to FIGS. 6A, 6B to 17. The A-A cross sectionalconfiguration indicates a cross sectional configuration of the padportion 5 and the optical black region 3 b whereas the B-B crosssectional configuration indicates a cross sectional configuration of theground connecting pad portion 5 g of the shield film.

First, as shown in FIGS. 6A, 6B, there is provided a structure includingthe Si semiconductor layer 10, the plurality of wiring layers 9 formedon the front-surface of the Si semiconductor layer 10, and thesupporting substrate 8 provided on the front-surface of the plurality ofwiring layers 9. The imaging region of the Si semiconductor layer 10includes two dimensionally arranged pixels formed of photodiodes 11 eachused as a photoelectric converter and a plurality of pixel transistors.A method of fabricating the structure includes forming the semiconductorlayer 10 and the plurality of wiring layers 9 on a separate substrate;bonding the supporting substrate 8 on a surface of the plurality ofwiring layers 9; and removing the substrate on which the semiconductorlayer 10 has been formed.

In the plurality of wiring layers 9, a plurality of interconnectsincluding those for signal circuitries and other components are formedvia the interlayer dielectric 14, for a material of which silicon oxidefilm (SiO₂) is used. FIG. 6A is one example of the plurality of wiringlayers 9 including four interconnects M1, M2, M3, M4, each of which isconnected to one of predetermined interconnects via a contact hall 13.In this embodiment, the interconnect M4 is wire-bonded to an externalconnection in the later-described pad portion 5. The interconnect M4 ismade of Aluminum (Al) so as to have an excellent connection with Aubonding wire. The first to third interconnects M1 to M3 can be madeeither of Al or Cu. If the interconnects M1 to M3 are made of Cu, theinterconnects M1 to M3 will exhibit excellent conductivity. Theplurality of wiring layers 9 in FIG. 6B also includes predeterminedinterconnects; however, only the ground interconnect 15 is illustratedin FIG. 6B. The ground interconnect 15 is placed so as to brought intocontact with the shield film in the later-described ground connectingpad portion 5 g, thereby setting potential of the shield film to becongruent with the ground potential. Since the cross sectionalconfiguration along the line B-B of the solid-state imaging device 1 inFIG. 2 excludes the effective pixel region 3 a and the optical blackregion 3 b, the photodiodes 11 are not formed on the Si semiconductorlayer 10.

Referring back to FIG. 6B, a nitride film (SiN) 12 forming theantireflective film 45 is formed on the entire surface of the Sisemiconductor layer 10. In this embodiment, the nitride film is used asthe antireflective film 45; however, the antireflective film 45 may beconfigured to include the nitride film and a hafnium oxide (HfO₂) filmstacked thereon.

In this embodiment, the front-surface of the solid-state imaging deviceis defined as a side forming the plurality of wiring layers 9 whereasthe rear-surface thereof is defined as a side forming the antireflectivefilm, in viewing from the Si semiconductor layer 10 on which thephotodiodes 11 are formed.

Next, as illustrated in FIGS. 7A, 7B, the openings 16 are formed byetching portions of the structure corresponding to the pad portion 5 andthe ground connecting pad portion 5 g. In FIG. 7A, the opening 16 isformed so as to expose the interconnect M4, whereas in FIG. 7B, theopening 16 is formed so as to expose the ground interconnect 15.

Next, as illustrated in FIGS. 8A, 8B, the silicon oxide (SiO₂) film 17is deposited on the surface of the nitride film 12. The silicon oxidefilm is deposited on a sidewall and a bottom of the opening 16. In thisembodiment, the antireflective film 45 is formed of a two-layered filmincluding the nitride film 12 and the silicon oxide film.

As illustrated in FIGS. 9A, 9B, the silicon oxide film 17 formed on thebottom of the opening 16 is selectively removed by etching. For example,after portions other than the bottom of the opening 16 have been maskedwith a resist film, the silicon oxide film 17 can be removed bydry-etching. The interconnect M4 and the ground interconnect 15 arere-exposed from the bottom of the opening 16 in this manner. Afterhaving selectively removed the silicon oxide film 17, the shield film isdeposited on the entire internal side-wall of the opening 16. Asexamples of a material for the shield film 18 having shieldingproperties, tungsten (W), aluminum (Al), molybdenum (Mo), iridium (Ir)can be given. The shield film 18 is deposited on the entire internalside-wall of the opening by sputtering process or CVD process. A shieldfilm deposited by sputtering process can exhibit more adhesiveness thana shield film made by CVD process. When the shield film is deposited bysputtering, the grain size of the material is relatively large; however,the grain size of the material is relatively small by CVD process,thereby improving the shielding properties of the material deposited byCVD process in comparison to that deposited by sputtering.Alternatively, the shield film may be deposited by sputtering and CVDprocessed in combination. In this embodiment, tungsten (W) is used as amaterial for the shield film 18.

Subsequently, as illustrated in FIGS. 10 A, 10B, the shield film 18placed on the upper portions of the effective pixel region 3 a and thepad portion 5 (see FIG. 2) is removed using a resist mask. The shieldfilm 18 is selectively deposited on the internal side-wall of theopening 16 excluding the portions of photodiodes 11 (light-receivingportion) in the effective pixel region 3 a and the pad portion 5 shownin FIG. 2.

For example, as illustrated in FIG. 10A, the shield film 18 is notdeposited on the opening 16 of the pad portion 5 but is deposited on theoptical black region 3 b. As illustrated in FIG. 10B, the shield film 18is deposited on the internal side-wall and the bottom of the opening 16of the ground connecting pad portion 5 g. The shield film 18 isconnected to the ground interconnect 15 at the bottom of the opening 16of the ground connecting pad portion 5 g. Thus, the potential of theshield film 18 formed is fixed to the same potential as the groundpotential. In this embodiment, the opening 16 is formed in the precedingstep to the step of depositing the silicon oxide film 17. Since one ofthe openings 16 is formed as the ground connecting pad portion 5 g thatexposes the ground interconnect and the shield film 18 is deposited onthe internal side-wall and the bottom of the opening 16 of the groundconnecting pad portion 5 g in the step of depositing the shield film 18,the potential of the shield film 18 is fixed to the same potential asthe ground potential. Since the silicon oxide film 17 is deposited onthe internal side-wall of the opening 16, the shield film 18 will notdirectly be in contact with the Si semiconductor 10 and the plurality ofwiring layers 9.

After the shield film 18 has been formed on the predetermined position,the passivation film 19 for planarization is deposited thereon asillustrated in FIGS. 11A, 11B. The passivation film is deposited on theentire surface including the internal side-wall and the bottom of theopening 16. As the passivation film 19, a silicon nitride (SiN) film canbe used, and a plasma nitride film can more preferably be used.

Next, as illustrated in FIGS. 12A, 12B, first resist layers 20 areplaced in the openings 16 that form the pad portion 5 and the groundconnecting pad portion 5 g.

As illustrated in FIGS. 13A, 13B, on-chip color filters CF are formedcorresponding to the photodiodes 11 in the effective pixel region 3 aand the optical black region 3 b (see FIG. 2.). In this embodiment, theon-chip color filters CF each corresponding to one of the colors R(red), G (green), B (blue) are formed so as to match with positions ofthe respective photodiodes 11. The on-chip color filters CF are formedby applying a resist for each color, exposing the resist, and developingthe resist. Since the effective pixel region 3 a and the optical blackregion 3 b are not shown in the cross sectional configuration in FIG.13B, the on-chip color filters CF are not illustrated in FIG. 13B.

As shown in FIGS. 14A, 14B, the on-chip microlens film 21 is applied onthe entire surface of the passivation film 19 including the surfaces ofthe on-chip color filters CF. The on-chip microlens film 21 is anorganic material, an example of which includes novolac resin. Thematerial is fabricated as an on-chip microlens in the subsequent step.

Next, as shown in FIG. 15A, having applied the on-chip microlens film21, a second resist layer 26 is formed on positions corresponding toeach of the on-chip color filters CF, and the second resist layer isthen exposed, developed, reflowed to form a structure of the on-chipmicrolens.

Finally, as shown in FIGS. 16A, 16B, the entire surface of the secondresist layer 26 is etched. As illustrated in FIG. 16A, a shape of theon-chip microlens film 21 is transformed into the shape of the secondresist layer 26 shown in FIG. 15A to form the on-chip microlenses 25 inthe effective pixel region 3 a and the optical black region 3 b.Further, with the etching process, the first resist layer 20 placed inthe openings 16 of the pad portion 5 and the ground connecting padportion 5 g is removed, thereby forming the openings 16 again. The firstresist layer 20 placed in the openings 16 is etched so as to expose theinterconnect M4 as shown in FIG. 16A whereas the first resist layer 20is etched so as not to etch the shield film 18 as shown in FIG. 16B. Theshield film 18 is exposed in the example shown in FIG. 16B; however,since the ground interconnect 15 has been in contact with the shieldfilm 18, small amounts of the passivation film 19 or other films can beremained on the shield film 18. Further, as shown in FIG. 16B, since thepassivation film 19, the on-chip maicrolens film 21, and the firstresist layer 20 are formed in this order on the shield film 18 on theinternal side-wall of the opening 16, moisture resistance of the shieldfilm 18 on the internal side-wall can be improved, thereby preventingdeterioration of the shield film 18.

In the pad portion 5 formed in this manner, the bonding wires 24 arewire-bonded with the interconnect M4 exposed from the bottom of theopening 16, thereby taking out the electrode to the outside. In thisembodiment, Au fine wires may be employed as the bonding wires 24.

In this embodiment, since a layer including the silicon oxide film 17,the passivation film 19, and the on-chip microlens film 21 is formed onthe internal side-wall of the opening 16, current will not be leakedfrom the bonding wires 24 via the Si semiconductor layer 10 due to thedifference in the potential between the areas in the Si semiconductorlayer 10. Moreover, since exposure of the interlayer dielectric 14 ofthe plurality of wiring layers 9 from the internal side-wall of theopening 16 can be prevented, absorption of moisture can be prevented inthe interconnects included in the plurality of wiring layers 9 and theinterlayer dielectric 14. Thus, the product reliability of thesolid-state imaging device increases with an increase of the moistureresistance of the plurality of wiring layers 9.

Further, in this embodiment; since the shield film 18 is connected withthe ground interconnect 15 in the ground connecting pad portion 5 g, thepotential of the shield film 18 is fixed to the same potential as theground potential.

In this embodiment, a method of fabricating a solid-state imaging deviceincludes forming the opening 16 including the pad portion 5 and theground connecting pad portion 5 g prior to depositing the insulatingfilm and the silicon oxide film 17, both forming the antireflective film45. Thus, the silicon oxide film 17 forming part of the antireflectivefilm 45 can be uniformly formed on the internal side-wall of the opening16. With this method, the shield film 18 and the bonding wires 24 willnot be in contact with the Si semiconductor layer 10 in a case where theshield film 18 and the bonding wires 24 are formed on the internalside-wall of the opening 16. In a case of forming the shield film 18 onthe antireflective film 45, if the ground connecting interconnect 15 hasbeen provided to the opening 16, the step of connecting the shield film18 to ground can simultaneously be carried out with the step ofdepositing the shield film 18. Since the shield film 18 on the internalside-wall of the opening 16 of the ground connecting pad portion 5 g iscovered with the passivation film 19 and on-chip microlens film 21, themoisture resistance of the shield film 18 can be improved, therebypreventing deterioration of the shield film 18.

The solid-state imaging device according to the embodiment, tungsten (W)is used as a material of the shield film 18; however, other materialssuch as aluminum (Al), molybdenum (Mo), ruthenium (Ru), and iridium (Ir)may also be used.

Next, FIG. 17 is a schematic diagram illustrating a solid-state imagingdevice according to a second embodiment of the invention. Thesolid-state imaging device according to this embodiment, aluminum isused as a material of the shield film, and the same reference numeralsas those used in FIGS. 4, 5 are used to denote the corresponding partsin FIGS. 17A, 17B, and duplicated descriptions thereof are thus omitted.The solid-state imaging device according to the second embodimentincludes the same configuration as that shown in FIG. 1. FIG. 17A showsthe A-A cross-sectional configuration while FIG. 17B shows the B-Bcross-sectional configuration in FIG. 2.

The solid-state imaging device according to the second embodiment ismanufactured in compliance with the fabricating steps for the firstembodiment; however, the location of depositing a shield film 22 in thesecond embodiment is different from that shown in the first embodiment.

In the second embodiment, an area of the shield film 22 corresponding tothe effective pixel region 3 a is etched in the similar manner as thefirst embodiment; however, an area of the shield film 22 correspondingto the opening 16 of the pad portion 5 is not etched. The shield film 22is partially removed to form an insulating portion 23 such that theareas of the shield film 22 corresponding to the opening portion 16 ofthe pad portion 5 is electrically insulated from other areas of theshield film 22 including those corresponding to the opening portion ofthe ground connecting pad portion 5 g. In this manner, the areas of theshield film 22 corresponding to the opening portion 16 of the padportion 5 is electrically cut off from other areas of the shield film 22formed on the ground connecting pad portion 5 g by forming theinsulating portion 23 in the shield film. Thus, according to thisembodiment, by having the insulating portion 23, the area of the shieldfilm 22 corresponding to the opening 16 of the pad portion 5 iselectrically insulated from the area of the shield film 22 correspondingto the ground connecting pad portion 5 g.

After the shield film 22 has selectively been formed in this manner, thepassivation filrm 19, on-chip color filters CF, and on-chip microlenses25 are formed in the similar steps as those conducted in the firstembodiment. However, in an etching step for forming the on-shipmicrolenses 25, the bottom of the opening 16 of the pad portion 5 isetched so as to expose the shield film 16 as shown in FIG. 17A. Thebottom of the opening 16 of the ground connecting pad portion 5 g isetched so as not to etch the shield film 22. The shield film 22 isexposed in the example shown in FIGS. 17A, 17B; however, since theinterconnect has been in contact with the shield film 22, small amountsof the passivation film 19 or other films can be remained on the shieldfilm 22.

As similar to the first embodiment, since the shield film made ofaluminum (Al) is brought into contact with the ground connectinginterconnect 15 exposed from the opening 16 in the ground connecting padportion 5 g, the potential in the area of the shield film 22corresponding to the ground connecting pad portion 5 g is fixed to thesame potential as the ground potential. The bonding wire 24 made of gold(Au) is connected to the external electrode and the interconnect M4 viathe shield film 22 in the opening 16 of the pad portion 5. In thisembodiment, the shield film 22 made of aluminum (Al) is alloyed with theboding wire 24 made of Au.

The internal side-wall of the opening 16 corresponding to the padportion 5 in this embodiment is coated with the shield film 22 formed ofmetal layers via the insulating film formed of the silicon oxide film17. Since one metal layer (shield film 22) is formed on the internalside-wall of the opening 16 of the pad portion 5 in this manner, it ispossible to reduce damage to the insulating film (silicon oxide film 17)formed on the internal side-wall of the opening 16 of the pad portion 5in wire bonding.

Further, the leak current can be prevented from flowing between thebonding wire 24 made of gold (Au) and the silicon layer 10 forming asemiconductor layer. Moreover, the interlayer dielectric 14 of theplurality of wiring layers 9 can be prevented from being exposed fromthe opening 16, and absorption of moisture in the metal interconnectsused in the plurality of wiring layers 9 and in the interlayerdielectric 14 can also be prevented. Further, the passivation capabilityof the insulating film (silicon oxide film 17) can be increased byforming the metal layer (shield film 22) on the internal side-wall ofthe opening 16 of the pad portion 5.

As described in the second embodiment, if a material used for the shieldfilm can be alloyed with a material for the bonding wire, the shieldfilm can be left on the internal side-wall and the bottom of the openingof the pad portion. In the embodiments having the aforementionedconfigurations, it is possible to improve the reliability of the padportion.

A camera may be formed with the solid-state imaging device 1 of theaforementioned first or second embodiment. FIG. 18 shows a cameraincluding the solid-state imaging device of the embodiment. The camera110 shown in FIG. 18 is configured to include the backside-illuminatedimaging device 1, an optical lens system 111, an input-output unit 112,a signal processor 113, and a central processing unit for controllingthe optical lens system as one assembly. Alternatively, thebackside-illuminated imaging device 1 can be configured to include theoptical lens system 111, the input-output unit 112, and the signalprocessor 113. Further, as another example, a camera 115 is configuredto only include the solid-state imaging device 1, the optical lenssystem 111, and the input-output unit 112. As still another example, acamera 116 is configured to include the solid-state imaging device 1,the optical lens system 111, the input-output unit 112, and the signalprocessor 113.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

1. A solid-state imaging device that receives incident light through abackside thereof, the solid-state imaging device comprising: asemiconductor layer on which a plurality of pixels includingphotoelectric converters and pixel transistors are formed; a wiringlayer on a first surface of the semiconductor layer; a pad portion on asecond surface of the semiconductor layer; an on-chip microlens layercarried on the second surface of the semiconductor layer; an opening inthe semiconductor layer exposing a conductive layer of the wiring layer;an insulating film extending from the second surface to an internalside-wall of the opening so as to insulate the semiconductor layer; anda light shield film on the insulating film, wherein, a portion of theon-chip microlens layer lines said internal side-wall of said opening inthe vertical direction, and a portion of the light shield film isremoved so that a portion of the light shield film coating said internalside-wall of said opening is insulated from a remainder of said lightshield film.
 2. A solid-state imaging device according to claim 1,further comprising a bonding wire connected to the conductive layerexposed at a bottom of the opening.
 3. A solid-state imaging deviceaccording to claim 1, wherein the insulating film includes anantireflective film.
 4. A solid-state imaging device according to claim1, wherein the insulating film includes an antireflective film, apassivation film, and an on-chip microlens film.
 5. A method offabricating a solid-state imaging device comprising: forming a wiringlayer on a first surface of a semiconductor layer having a plurality ofpixels including photoelectric converters and pixel transistors; formingin the semiconductor layer an opening corresponding to a pad portion ofa second surface of the semiconductor layer so as to reach a conductivelayer of the wiring layer; forming an insulating film extending from thesecond surface to an internal side-wall of the opening so as to insulatethe semiconductor layer; forming a light shield film on said insulatingfilm with a portion thereof removed so that a portion of the lightshield film coating said internal side-wall is insulated from aremaining portion of said light shield film; and forming an on-chipmicrolens layer on said second surface of said semiconductor layer suchthat a portion of said on-chip microlens layer lines said internalside-wall of said opening in the vertical direction.
 6. A method offabricating a solid-state imaging device according to claim 5, furthercomprising: connecting a bonding wire to the conductive layer exposed ata bottom of the opening.
 7. A method of fabricating a solid-stateimaging device according to claim 5, wherein in the step of forming theinsulating film, using an antireflective film as the insulating film. 8.A camera comprising: a solid-state imaging device; an optical lens; anda signal processor, wherein, the solid-state imaging device includes (a)a semiconductor layer on which a plurality of pixels includingphotoelectric converters and pixel transistors are formed; (b) a wiringlayer on a first surface of the semiconductor layer; (c) a pad portionon a second surface of the semiconductor layer; (d) an on-chip microlenslayer on said second surface of the semiconductor layer; (e) an openingin the semiconductor layer that reaches a conductive layer of the wiringlayer; (f) an insulating film extendedly formed from the second surfaceto an internal side-wall of the opening so as to coat the semiconductorlayer; and (g) a light shield film formed on the insulating film,wherein, a portion of said on-chip microlens layer lines said internalside-wall of said opening in the vertical direction, and a portion ofthe light shield film is removed so that a portion of the light shieldfilm coating said internal side-wall of said opening is insulated from aremainder of said light shield film.